Mr Kerry said he remained optimistic a deal could be reached through the Geneva talks with Iran, despite the last-minute collapse at the weekend.

Israel and hawks in the US Congress have spoken out against a short-term agreement that would allow Iran to continue enriching uranium at low levels, which could be used in power stations but not as part of a nuclear arms programme.

"What we are doing will protect Israel more effectively," Mr Kerry said during a visit to the United Arab Emirates.

According to Mr Kerry, the P5+1 group, representing the five permanent members of the UN Security Council plus Germany, were united when the proposed deal was presented to the Iranian negotiating team on Saturday.

"But Iran couldn't take it; at that particular moment they weren't able to accept," Mr Kerry said.

"Our hope is that in the next months we can find an agreement that meets everyone's standards."

According to officials in the Obama administration, Washington had been prepared to relax economic sanctions and free some of Iran's assets if Tehran was prepared to freeze its nuclear programme for six months.

It is understood the deal would have also required Iran to convert its existing stockpile of material into harmless oxide.

The Iranians would have also agreed not to activate its plutonium reactor at Arak, which could be used to enhance a nuclear arms programme, during the six-month freeze.

Meanwhile, Iran was taking other steps to show its willingness to compromise.

An Iranian news agency reported that the country and International Atomic Energy Agency had agreed a "roadmap for co-operation''.

The agreement with the UN nuclear watchdog was announced at a joint press conference in Tehran. Under the agreement, the agency will be allowed to send inspectors to the heavy water production plant in Arak, as well as the Gachin uranium mine in the south.

However, no agreement appears to have been struck which will allow visits to the Parchin military base, where intelligence sources say weapons research may have been carried out.